[Dnsmasq-discuss] [PATCH] forward.c: fix handling of truncated response

[Niels Hendriks]

Hi all,


I believe we are affected by this bug and had to downgrade to 2.89 on our Debian installation.


I see it has been a few months since the last message regarding this issue. I'm just a normal user and a little bit confused on how to proceed.
Is this something that is still being worked on, and is there an expectation of when the new version will be released that fixes this issue? Or is there something wrong with the program performing the DNS requests and should I ask them to fix something on their side to handle what is happening here?


Thanks in advance!
Niels Hendriks



 From:   Rahul Thakur via Dnsmasq-discuss <dnsmasq-discuss at lists.thekelleys.org.uk> 
 To:   <dnsmasq-discuss at lists.thekelleys.org.uk> 
 Sent:   04/10/2024 1:33 PM 
 Subject:   [Dnsmasq-discuss] [PATCH] forward.c: fix handling of truncated response 

From: Rahul Thakur <rahul.thakur at iopsys.eu> 
 
The handling of truncated reponse is broken in 2.90. The answers 
are removed before forwarding in case TC bit is set, which 
seems incorrect as per rfc 5625. 
A combined reading of section 4.4.1 of rfc 5625 section 6.1.3.2 
of rfc 1123 suggests when dnsmasq explicitly deletes the answers 
in a truncated response, then it deprives clients that do not fallback 
to TCP and are happy with the truncated UDP response to be able 
to resolve the queries. In light of this, it sounds like a better 
strategy is to forward the truncated UDP response as is to the client, 
and let the client decide what action it wants to take. 
 
Signed-off-by: Rahul Thakur <rahul.thakur at iopsys.eu> 
--- 
 src/forward.c | 3 --- 
 1 file changed, 3 deletions(-) 
 
diff --git a/src/forward.c b/src/forward.c 
index 10e7496..1ede913 100644 
--- a/src/forward.c 
+++ b/src/forward.c 
@@ -785,9 +785,6 @@ static size_t process_reply(struct dns_header *header, time_t now, struct server 
   if (header->hb3 & HB3_TC) 
     { 
       log_query(F_UPSTREAM, NULL, NULL, "truncated", 0); 
-      header->ancount = htons(0); 
-      header->nscount = htons(0); 
-      header->arcount = htons(0); 
     } 
  
   if  (!(header->hb3 & HB3_TC) && (!bogusanswer || (header->hb4 & HB4_CD))) 
--  
2.25.1 
 
 
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